1. Field of the Invention
The present invention relates to an apparatus for continuously producing electric-welded steel tubes or pipes by continuously supplying coiled strips as connected to one another by welding, progressively forming the strip into a tubular shape and high-frequency welding the butting edges of the strip to form a seam.
2. Description of the Prior Art
Apparatus are known for continuously producing steel pipes by progressively forming a steel strip into a tubular shape and welding together the opposed edges of the strip as disclosed in U.S. Pat. No. 4,339,938.
However, the conventional continuous production apparatus, which are suited for producing a large quantity of steel pipes of specified diameter, are inefficient to produce small quantities of steel pipes having varying diameters and wall thicknesses because all the forming rolls, welding rolls and sizing rolls must be replaced every time steel pipes of different diameter are to be produced. In fact, the replacement procedure entails the necessity of holding the apparatus out of operation frequently even for an entire day. The forming rolls, welding rolls and sizing rolls need to be replaced promptly while the apparatus is out of operation.